Environmental decay of polymers

Environmental stress cracking or corrosion (ESC) is the phenomenon that materials fail, in the presence of relatively inert chemical agents (liquids or gasses) and /or radiation, at much lower stresses, than in their absence, under the formation of many little cracks. We distinguish real chemical corrosion and stress corrosion, each with its own characteristics. 

Stress corrosion can be subdivided in chemical and physical corrosion  

Under the influence of stresses chemical reactions take place leading to chain fracture. Examples are 

The environment that causes this kind of corrosion is often rather inert the polymer does not dissolve or swell, but there is some diffusion of liquid or gas, in particular at the surface. If the diffusion rate is small localised plasticization is possible and subsequently deformation is caused by the stresses. This leads to increased plasticization and to the formation of crazes and even of cracks. 

11 Critical corrosion stress as a function of pH (after Van den Heuvel and Klop, 2002). 

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The environmental decay of polymers in liquids is primarily dependent on the solubility parameters of polymer and liquid and on the hydrogen bond interaction between polymer and liquid. 

The remainder of this section on environmental decay of polymers is devoted to the physical interaction between polymer and environment. This is what in general is called "environmental stress cracking", which thus is only one part of the story. 

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